Technical Field
The present invention relates to a printing apparatus, a printing method, and an ink set.
Description of Background Art
Inkjet printers are in wide use in a variety of fields. Wider applications and improving performance of inkjet printers have created a demand for high-quality inkjet printing.
One way of achieving high-quality printing with an inkjet printer is to reduce the volume of ink droplets ejected from inkjet heads. A problem, however, is that this method involves misting, which occurs during the ejection of ink droplets from the inkjet heads to the media when the ejected ink droplet volume is excessively small. This makes it difficult to reduce the ink droplet volume when the volume is equal to or smaller than, for example, about 1 pl (picoliter).
Recently, a technique that uses a plurality of inks of different concentrations for printing of the same color has attracted interest as a method of further improving print quality without changing ink droplet volume. Specifically, for example, a method is known in which lighter color inks are used for the magenta (M) and cyan (C) colors of YMCK inks, in addition to using these inks in normal concentrations (see, for example, U.S. Pat. No. 4,952,942).
When a high-concentration ink (hereinafter, “dark ink”) and a low-concentration ink (hereinafter, “light ink”) of the same color are used, a sufficiently high concentration and a sufficiently low concentration are desired for the dark ink and the light ink, respectively, when, for example, printing accuracy is to be improved over a wider brightness range. It is also desired to sufficiently increase the concentration of the dark ink when, for example, prints are to be made in high concentration with a thin ink layer. However, there are potential problems associated with increasing dark ink concentration and decreasing light ink concentration.
For example, a pigment may be used as a colorant to increase dark ink concentration. Here, increasing the pigment content for increased concentration increases the risk of, for example, pigment aggregation, and may fail to properly produce ink. In addition, ink droplets cannot be properly ejected through inkjet heads when, for example, ink viscosity is increased to prevent pigment aggregation. It is thus not always easy to sufficiently increase dark ink concentration when using gradation inks.
The light ink can have sufficiently low concentrations, for example, when a pigment of small particle diameter is used, or when a dye is used as the colorant. However, this may lower the weather resistance of the ink, for example, with respect to light and water, etc. Indeed, it is not always easy to, for example, sufficiently lower light ink concentration when using gradation inks.
In using gradation inks, there is a need for more appropriate ways of making high-quality prints with dark and light inks of more desirable properties. The present invention provides a printing apparatus, a printing method, and an ink set as a solution to the foregoing problems.